Subsea vehicle assisted pipeline commissioning method

ABSTRACT

The present invention is directed to a method for completing the commissioning of a subsea pipeline by purging with a compressed gas to dewater and dry the line wherein the operation is done on the seabed. More specifically, the method is carried out with a subsea vechicle (hereinafter “SV”) that powers pumps located on the seabed or are carried by the SV to inject/remove chemical, dewater, and dry, the pipeline. The present invention may be part of the commissioning of a new or old pipeline or a new portion of a pipeline in which a purging of the line with a compressed gas and drying of the line is required. After commissioning, product flows through the pipeline.

RELATED APPLICATION

[0001] This application is based on U.S. provisional application No.60/275,215, filed Mar. 13, 2001, entitled “Subsea to Subsea RemotelyOperated Vehicle Assisted Pipeline Commissioning Method”.

FIELD OF THE INVENTION

[0002] The present invention is directed to commissioning methods forsubsea pipelines. More specifically, the present invention is directedto a commissioning method wherein the operation is carried out on theseabed rather than at the surface.

BACKGROUND OF THE INVENTION U.S. Pat. No. 5,883,303 discloses anddescribes an apparatus and method for pigging, flooding and pressuretesting pipelines.

[0003] The above patent is directed to the testing required when a newpipeline is placed in operation. However, when commissioning a subseapipeline, or adding a new segment to an existing offshore pipeline, itis often desired to follow the hydrostatic pressure testing with aninert gas or specified medium to purge/dewater the subsea pipeline,and/or inject specified chemicals, to dry the inside of the line beforeflow of the oil/gas in the pipeline.

[0004] The dewatering of a subsea pipeline by the prior art has been atsurface level, usually on a surface vessel, boat, structure or platform.This requires that long lines of coiled tubing, hose, or pipe, be used.The prior art method uses large distances of coiled tubing, hose, orpipe, to connect the pipeline to a pump mobilized on the deck of asupport vessel to remove the water and dry the line before product isallowed to pass through the line. Also required by the prior art methodare large pumps, compressors, compressor boosters and surface supportvessel and/or vessels, to support the large volume of compressed gasesand fluids pumped through the significant distances to fill the newportion of the pipeline with the gas and fluids.

[0005] The method of the present invention eliminates the larger volumeof compressed gas and fluids, the higher pressure of the compressed gasand fluids, the large pumps/compressors, compressor boosters, longdistances of coiled tubing/hose/pipe, and substantial surface supportvessel/vessels, all required by the prior art methods.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a method for completing thecommissioning of a subsea pipeline by purging with a compressed gas todewater and dry the line wherein the operation is done on the seabed.More specifically, the method is carried out with a subsea vechicle(hereinafter “SV”) that powers pumps located on the seabed or that arecarried by the SV to inject/remove chemical, dewater, and dry, thepipeline. The present invention may be part of the commissioning of anew or old pipeline or a new portion of a pipeline in which a purging ofthe line with a compressed gas and drying of the line is required. Aftercommissioning, product flows through the pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a schematic view of a surface support vessel positionedto serve a subsea pig launcher/receiver on a manifold on the seabed anda subsea pig launcher/receiver on a second manifold connected by aportion of a subsea pipeline;

[0008]FIG. 2 is a schematic view of a subsea pig launcher/receiverstabbed into a manifold on the seabed and a SV carrying a fill and testpackage of equipment to carry out a commissioning method;

[0009]FIG. 3 is a view of one possible panel face connected to thesubsea pig launcher/receiver and a representative schematic of thevalves included in the panel for carrying out a commissioning method;

[0010]FIG. 4 is a schematic view of a subsea pig launcher/receiverstabbed into a manifold on the seabed and assisted by a SV;

[0011]FIG. 5 is a view of one possible panel face connected to thesubsea pig launcher/receiver and a representative schematic of thevalves included in the panel for carrying out a commissioning method;

[0012]FIG. 6 is a representative schematic view of the pump of the filland test package of equipment connected at one subsea piglauncher/receiver pushing the pig through the pipeline to the subsea piglauncher/receiver at the other end of the pipeline;

[0013]FIG. 7 is a schematic of the SV tethered from the support vesseland powering the pump to push the pig through the subsea pipeline to asubsea pig launcher/receiver;

[0014]FIG. 8 is a representative schematic of the subsea piglauncher/receiver where the pig has arrived in the receiver;

[0015]FIG. 9 is a representative schematic of the SV attaching thepressure pump to asubsea pig launcher/receiver to perform ahigh-pressure hydrostatic test on the pipeline;

[0016]FIG. 10 is a schematic of the SV disconnecting the pressure pumpto the subsea pig launcher/receiver after completeing the high-pressurehydostatic commissioning test and opening a valve to release thepressure in the pipeline;

[0017]FIG. 11 is a representative schematic of the SV attaching acompressed gas source to one subsea pig launcher/receiver to force thepig through the pipeline from the launcher to the subsea pig receiver;

[0018]FIG. 12 is a schematic of the SV attaching the dewatering pump andremoving the water from the pipeline to move the pig through thepipeline from one pig launcher/receiver to the second subsea piglauncher/receiver;

[0019]FIG. 13 is a schematic of the SV tethered from the support vesseland powering the pump at one subsea pig launcher/receiver to reduce thepressure on the launcher side of the pig which enables the compressedgas to push the pig toward the receiver;

[0020]FIG. 14 is a schematic of the SV at one subsea piglauncher/receiver to disconnect the compressed gas source after fillingthe pipeline with gas; and

[0021]FIG. 15 is a schematic of the completed dewatered pipeline and therecovery of the SV and other equipment as required, to the supportvessel.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

[0022] Offshore drilling for oil/gas is continuing to expand at furtherdistances from shore and at greater depths. Subsea pipelines areutilized to transport the discovered product to a variety of dispositionpoints. These points include existing or new offshore trees, manifolds,pipelines, platforms, or onshore facilities. As new wells are completedsubsea pipelines flowing the product are tied through manifolds toexisting pipelines that are already in place to bring the product toshore. As dictated by law, the new sections of pipeline requirehydrotesting to make certain that the line has no leaks and in somecases, contains no water. In addition to hydrotesting, other steps inthe commissioning of the pipeline may be required, including dewatering,drying, cleaning, and installing chemicals. The present inventionrelates to any or all the steps as related to the commissioning of thesesubsea pipelines carried out on the seabed rather than at the surface.

[0023] Once a well is completed, a pipeline is connected to the well formoving the product to shore. The pipeline is often not extended all theway to shore but is tied through a manifold or connection to offshorefacilities. Manifolds as used herein may have a variety of specificstructures; however, the common function for the purpose herein is thatsections of pipelines are connected to other facilities, including otherpipelines via various connection assemblies referred to herein asmanifolds. Also common to a manifold as used herein is that there isstructure to provide internal access to the pipeline. The subseaperformance or operation of the commissioning method, the presentinvention, will be described as a method of commissioning a pipelinebetween two manifolds; however, it is understood that the commissioningis not limited to that portion of a pipeline between two manifolds butincludes any subsea pipeline or pipeline segment, most particularly onewhich has or could have both ends at the seafloor at the time of testingand commissioning

[0024] The present invention is directed to a commissioning methodwherein the operation is carried out on the seabed rather than at thesurface. It is illustrated by using a subsea vehicle to assist in theoperation and assumes that valves require to be mechanically operatedfrom the subsea vehicle. This is only one embodiment of the inventionsince the degree of assistance necessary by the subsea vehicle may bematerially reduced with the use of automated valves not requiringmechanical operation. The subsea vehicle need not carry the pumps areother equipment as shown in the embodiment illustrated by the drawings.

[0025] Referring to FIG. 1, a surface support vessel (or multiplevessels if required) 10 is positioned at the surface between twomanifolds 12 and 14. A subsea pipeline 16 is connected to the manifolds12 and 14. The vessel 10 supports the commissioning (the internalcleaning of the pipeline, the hydrostatic testing for leaks and theremoval of water and the partial product fill) of pipeline 16 beforeproduct is allowed to transported by pipeline 16 for passage to shore.The commissioning process is assisted by a subsea vehicle (SV) 18. TheSV may be a remotely operated vehicle (ROV) or autonomous underwatervehicle (AUV) as these vehicles are known in the prior art, or they maybe modified for the purposes of the present invention, or may includeany manned or unmanned vehicle that has a system that can manipulate thehoses, pumps and other equipment used in the commissioning method. TheSV 18 may be tethered to the support vessel 10 and may have a tethermanagement system (TMS) assuring that the tether is not in the way ofany operation. The SV 18 provides the electrical system for it'soperation and other equipment, as will be described hereinafter.Alternatively, an electrical umbilical cord may be part of the tetherand tether system. The SV 18 installs, by use of it's robotic arm 19, asubsea pig launcher/receiver 20 on manifold 12 (it being understood thatthe direction of operation is not material and the launcher/receiver maybe placed on manifold 14). In an equally desirable embodiment, the piglauncher/receiver may be installed on the pipe end and laid with thepipe at the time the pipeline is laid. The pig launcher/receiver 20 isshown as stabbed into the top of manifold 12; however, piglauncher/receiver 20 may be in any orientation. The SV 18 then installsa subsea pig launcher/receiver 30 on manifold 14. Similarly, thisassembly may also be installed on the pipe end before the pipe is laid,and then laid with the pipeline. Pig launcher/receiver 20 is installedwith a pig 22, which is a known structure used in cleaning ormaintaining fluids separate in a pipeline, in the launcher/receiver 20(see FIG. 2). Pig launcher/receiver 20 and pig receiver 30 can each havea panel 24 and 34, respectively, that is operated by the robotic arm 19(see FIG. 2) on the SV 18. Pig launcher/receiver 20 and receiver 30 mayalready be installed or may have been installed as part of the pipelineinstallation.

[0026] The SV 18 returns to the support vessel, (if required), 10 aftercompleting the installation of the pig launcher/receiver 20 and the pigreceiver 30 to acquire a fill and test package 40 which includes anumber of pumps and lines that are connected to either panel 24 or 34 aswill be described in more detail hereinafter. The package 40 ispreferably held by the SV 18 during the remainder of the commissioningprocess; however, landing the package 40 on the sea floor near piglauncher/receiver 20 is also an alternative. The fill and test package40 may alternatively be more than one package mounted on differentskids.

[0027] Referring now to FIG. 2, manifold 12 is at one end of pipeline 16and may have one or more other pipelines connected at manifold 12. Thesubsea pig launcher/receiver 20 is connected to the manifold in anyorientation that allows access to pipeline 16. A pig 22 is in the piglauncher/receiver 20. A panel 24 (see FIG. 3) on pig launcher/receiver20 contains passageways, valves and gauges to control the flow of fluidsand gasses through pipeline 16. The robotic arm 19 on the SV 18, orother suitable control provision, begins the flow of water behind pig 22by opening free flooding valve 51 to force the pig 22 through pipeline16 to clean any solid debris that remains in the pipeline after beinglaid in place. Upon opening valve 51 in panel 24, seawater entersthrough opening 52 of a filter 54, where the seawater is filtered andchemical may be injected, and passes through panel 24 and out opening 55before pushing pig 22 through pipeline 16 until the pressure on eitherside of the pig equalizes. A check valve (not shown) on the pig receiver30 allows the air in front of the pig to exit the receiver side of thepipeline 16. The SV 18 then moves to the pig receiver 30.

[0028] Referring now to FIG. 4, manifold 14 may have a vertical sectionto which the subsea pig receiver 30 is connected so as to have access topipeline 16. A panel 34 (see FIG. 5) on pig receiver 30 containspassageways, valves and gauges to control the flow of fluids throughpipeline 16. The SV 18 opens the discharge valve 61 of panel 34. It isrecognized that the method described assumes that each panel 24 and 34requires the assistance of the SV 18 to open and close the valves;however, if the valves on either panel are automated and are operatedfrom the surface or the SV 18, then the SV need not make trips from thepig launcher/receiver 20 to the pig receiver 30 as described. The SV 18then moves to the pig launcher/receiver 20. It is recognized that thespecific sequence of events will depend upon the requirements ofspecific applications, and that the sequence stated here isrepresentative but is not the only method in which the described systemmay be operated.

[0029] Referring to FIG. 6, the SV 18 then closes free flowing valve 51on the panel 24. A line 42 from the fill and test package 40,specifically from a high volume pump, is connected to port 56 on thepanel 24 and valve 57 is opened. Seawater is pumped through line 42 andthe panel 24 and out opening 55 to force pig 22 toward the pig receiver30.

[0030] The operation of filling the pipeline 16 with seawater pumpedfrom pig launcher/receiver 20 to pig receiver 30 is illustrated in FIG.7. An aspect of the present invention is that the pumping is done fromthe fill and testing package 40 held by SV 18, or placed on the seabed,rather than pumps mobilized on board the surface support vessel 10 Thus,the entire operation is done subsea rather than using the long lines andlarge equipment that is necessary if done on the surface. The umbilicalfor the SV 18 may be thousands of feet long and the subsea operation ofthe present invention eliminates those number of feet of coiled tubingusually used in this operation. Pumping is continued until the pig 22arrives in the pig receiver 30. Arrival of the pig at the receiver isdetected by any of a variety of pig detectors commonly known in theindustry, and an indication of arrival can be sensed from pressurechanges or transients at the launcher/receiver. The SV 18 then moves tothe pig receiver 30.

[0031] Referring now to FIG. 8, the SV 18 positioned at the pig receiver30 closes valve 61 on panel 34 in preparation for the hydrostatictesting of pipeline 16. The SV 18 then moves to the piglauncher/receiver 20.

[0032] Referring now to FIG. 9, SV 18 uses robotic arm 19 to stab line42 from the fill and test package 40, specifically from a high pressurepump, into the hot stab 56 on the panel 24 and valves 57 and 60 areopened. It is recognized that, depending on the specific application, itmay be preferred to perform these steps in a different sequence, and itmay be preferred to connect the pump to either the launcher/receiver orreceiver end of the pipeline for hydrostatic testing. Seawater is pumpedthrough line 42 to increase the pressure in the pipeline 16 to testinglevel. The pressure is monitored by pressure gauge 58 and data recorder63. The test pressure is maintained for a length of time to make certainthat there are no leaks in the pipeline 16. Any drop in pressureindicates a problem and the first measure may be to repressure to testpressure and wait another length of time to make certain the pipeline 16will maintain pressure.

[0033] Upon successful completion of the hydrostatic testing of thepipeline 16, the SV 18 disconnects line 42, referring now to FIG. 10,and closes valve 57 and 60 and vents the pipeline through a flowrestrictor and/or free flooding valve 51 on the panel to depressure thepipeline 16. The flow of the water in the pipeline 16 will exit throughvalve 51; however, the flow is controlled and measured by flow meter 59so that the de-pressurization is slow and even and does not cause anyvibrations or other disturbances to the pipeline 16. Monitoring of thepressure gauge 58 and flow meter 59 as the flow of water is throughopening 55 and valve 51 is maintained until the internal pressurereaches ambient pressure, meaning that the pressure inside and outsidethe pipeline 16 are the same. The SV 18 then moves to the pig receiver30.

[0034] Referring now to FIG. 11, a compressed gas pack (gas source thatmay be nitrogen or air) 70, is connected to the pig receiver 30. The gaspack may be mounted to manifold 14, laid on the subsea floor, orconnected by a hose/tubing line from a remote site or from the surfacepreviously or at this time in the operation. The connection may be madeby any suitable method, including using the robotic arm 19 of the SV 18to stab the line 72 from the pack 70 into the hot stab 66 in panel 34and compressed gas inlet valve 67 is opened to force in the compressedgas behind the pig 22. The SV 18 then moves to the pig launcher/receiver20.

[0035] Referring now to FIG. 12, SV 18 uses robotic arm 19 or othersuitable method to connect line 42 from the fill and test package 40,specifically from the dewatering or vacuum pump, into port 56 of thepanel 24. The valve 57 is opened and the pipeline 16 is dewatered.Seawater is pumped through opening 55, valve 57 and line 42, reducingthe pipeline internal pressure at the launcher/receiver end so that amodest volume of compressed gas can push pig 22 by differential pressuretoward the pig launcher/receiver 20.

[0036] The operation of dewatering and pigging the pipeline 16 bypumping water through the pig launcher/receiver 20 from pipeline 16 isillustrated in FIG. 13. An aspect of the present invention is that thepumping is done from the fill and test package 40 held by SV 18 ratherthan pumps mounted on the support vessel 10. The operation being donesubsea eliminates the long lengths of coiled tubing, hoses, or piping,and the large pumps that are necessary when the operation is done at thesurface. The volume of compressed gas is significantly reduced. Sincethe gas in the pipeline is at a relatively low pressure, significantlysmaller quantity of compressed gas is required as compared to prior art.An additional advantage is that a smaller support vessel may beutilized. The operation of dewatering and pigging, meaning that thewater is forced out of pipeline 16 by the pig 22 being pushed bycompressed gas, until equilibrium is reached then the pig is drawn tothe launcher/receiver by the dewatering pump until the pig 22 arrives atthe pig launcher/receiver 20 at which time there is no further water tobe sucked out of the pipeline 16. The SV 18 then shuts off thedewatering pump and closes valve 47 on the panel 24. The pipeline 16 isnow ready for product to be passed through the pipeline 16. The productwill not be contaminated by water and the nitrogen or other compressedgas does not materially affect the product. The SV 18 disengages line 42and makes any necessary securing of manifold 12 as is deemed necessaryor desirable. The SV 18 then moves to the pig launcher/receiver 30.

[0037] Referring now to FIG. 14, the SV 18 closes valve 67 anddisengages compressed gas line 72 from panel 34. The compressed gas pack70 is made secure or connected to the SV 18 to be returned to surface.The SV 18 makes any necessary securing of manifold 14 as is deemednecessary or desirable. The commissioning operation that includescleaning, hydrostatic testing and dewatering is complete. It isunderstood that all steps are not necessary if the operation includesless than the commissioning operation as set forth. Additionally, anadditional step may be included whereby the product is introduced intothe pipeline.

[0038] Referring now to FIG. 15, the SV 18 carrying the fill and testpackage 40 is recovered to the support vessel 10.

[0039] The commissioning operation has been described in detail, but itis understood that this detail is representative, and that variations inthe method may be appropriate for specific applications. Significantimprovements to the prior art have been set forth. Modifications andadditions may be added without changing the commissioning operation asset forth. For example the commissioning method is carried out on apipeline with both ends on the seafloor or one end on the seafloor andthe operation is carried out at that end before the pipeline isconnected to manifolds or other structure. Another example, the panel 24may have a valve 67 that when open provides access to vacuum gauge 69.The robotic arm 19 and pumps on the fill and test package 40 are poweredby electric or hydraulic power. The tether connecting the support vessel10 includes a substantial electrical source that powers the pumps on thefill and test package 40 directly or powers a hydraulic power sourcewhich then drives the pumps. There may be three separate pumps on thefill and test package 40 or two pumps, the low volume high pressure pumpbeing able to operate both to add water to the pipeline 16 or as adewatering pump to suck water from the pipeline 16, or just one pump.There are many changes in details that may be made such that watertreating may be added, filters may be added, more than one pig may beused, methanol or other chemicals may be added between pigs, the pig mayinclude tracking means to name some; however, changes in detail do notchange the method as set forth and described.

1. A method of dewatering a pipeline between two subsea manifolds usinga source of compressed gas at one of said manifolds having a subsea piglauncher/receiver with a pig therein comprising: connecting a line fromsaid compressed gas source to said pig launcher/receiver for flow ofcompressed gas to force said pig to said other manifold; and connectinga dewatering pump which is subsea near said other manifold to draw waterfrom said pipeline and move said pig and compressed gas through thepipeline to said manifold.
 2. A method according to claim 1 wherein saidconnecting of said line and said vacuum pump is done with a robotic armmounted on a SV.
 3. A method according to claim wherein said dewateringpump is carried by said SV
 4. A method of dewatering a pipeline betweentwo subsea manifolds using a compressed gas pack connected to one ofsaid manifolds having a subsea pig launcher/receiver with a pig thereincomprising: drawing water, said pig and compressed gas through saidpipeline with a subsea pump at said other manifold.
 5. A methodaccording to claim 4 wherein said pump is carried by a SV.
 6. A methodaccording to claim 5 wherein said SV is tethered to a support vessel onthe surface.
 7. A method of cleaning and/or hydrostatic testing apipeline between two subsea manifolds, one of said manifolds having asubsea pig launcher/receiver with a pig and the other having a subseapig receiver comprising: using a SV to operate pumps on a fill and testpackage to force seawater behind said pig and move the pig from the piglauncher/receiver to the pig receiver; and pumping more water into saidpipeline to a test pressure and maintaining said pressure to assure thatthere are no leaks in said pipeline.
 8. A method according to claim 7wherein the test pressure is read on a gauge mounted on a panel on saidpig launcher/receiver.
 9. A method according to claim 8 wherein saidfill and test package is carried by said SV.
 10. A method forcommissioning a subsea pipeline while both ends are on the subsea floorbetween two subsea manifolds, one of said manifolds having a subsea piglauncher/receiver with a pig and the other having a subsea pig receivercomprising: using a SV, operating pumps on a fill and test package toforce seawater behind said pig and move the pig from the piglauncher/receiver to the pig receiver; pumping more water into saidpipeline to a test pressure and maintaining said pressure to assure thatthere are no leaks in said pipeline; using a SV, connecting a line froma compressed gas pack to said pig launcher/receiver for flow ofcompressed gas to force said pig to said pig launcher/receiver; andpumping using a dewatering pump to suck water from said pipeline andmoving said pig and compressed gas through the pipeline to said piglauncher/receiver.
 11. A method according to claim 10 wherein said SVhas a robotic arm for connecting and disconnecting pumps to saidpipeline.
 12. A method for the hydrostatic testing of a pipeline beforeits ends are connected wherein both ends are on the seafloor and havinga pig launcher/receiver at both ends of said pipeline; comprising: usingat least one subsea water pump to propel at least one pig down the lineand to raise the internal pressure of the pipeline sufficiently forhydrostatic testing of the pipeline.
 13. A method for dewatering apipeline before its ends are connected, wherein both ends are on theseafloor, and having a pig launcher/receiver at both ends of saidpipeline comprising: using at least one subsea water pump to pump thewater from the pipeline while injecting sufficient compressed gas topropel drying pigs down the pipeline.